Hardware device for processing the tasks of an algorithm in parallel

ABSTRACT

A hardware device for processing the tasks of an algorithm of the type having a number of processes the execution of some of which depend on binary decisions has a plurality of task units ( 10, 12, 14 ), each of which are associated with a task defined as being either one process or one decision or one process together with a following decision. A task interconnection logic block ( 16 ) is connected to each task unit for communicating actions from a source task unit to a destination task unit. Each task unit includes a processor ( 18 ) for processing the steps of the associated task when a received action requests such a processing. A status manager ( 20 ) handles actions coming from other task units and builds actions to be sent to other task units.

TECHNICAL FIELD

The invention relates to processing of algorithms used in the searchengines of a large data communication network such as the Internet, andrelates more particularly to hardware devices for processing the tasksof any algorithm in parallel.

BACKGROUND

The World Wide Web (WWW) provides accesses to a large body ofinformation. Compared with traditional databases, Web information isdynamic and structured with hyperlinks. Also, it can be represented indifferent forms and is globally shared over multiple sites andplatforms. Hence, querying over the WWW is significantly different fromquerying data from traditional databases, e.g. relational databases,which are structured, centralized and static. Traditional data bases cancope with a small number of information sources; but it is ineffectivefor thousands.

Most Web documents are text-oriented. Most relevant information isusually embedded in the text and can not be explicitly or easilyspecified in a user query. To facilitate Web searching, many searchengines and similar programs have been developed. Most of these programsare database based meaning that the system maintains a database, a usersearches the web by specifying a set of keywords and formulating a queryto the database. Web search aids are variously referred to as catalogs,directories, indexes, search engines, or Web databases.

A search engine is a Web site on the Internet which someone may use tofind desired Web pages and sites. A search engine will generally returnthe results of a search ranked by relevancy. A competent Web searchengine must include the fundamental search facilities that Internetusers are familiar with, which include Boolean logic, phrase searching,truncation, and limiting facilities (e.g. limit by field). Most of theservices try more or less to index the full-text of the originaldocuments, which allows the user to find quite specialized information.Most services use best match retrieval systems, some use a Booleansystem only.

Web search engines execute algorithms having internal processes whichare repetitive tasks with independent entry data. A classical step bystep processing of all processes and decisions on one entry data beforeprocessing the next entry data is inefficient since it takes too muchtime to process all the data. Thus, it is common to perform a search ofa pattern within each file of a disk. The main repetitive processes toperform are: load file, open file, scan each word and compare formatching with a pattern, append the result in a temporary file, closefile.

One way to improve the performance, and in particular to improve thesearch response time, is to achieve parallel processing by parallelizingthe search mechanism in the database or index table. Such softwareparallelization will be more optimized but is nevertheless limitedinsofar as the software processing, even if parallelized, requires aminimum of time which cannot be reduced.

SUMMARY OF THE INVENTION

Accordingly, the object of the invention is to provide a hardware assistdevice able to run a set of repetitive processes using local pipeliningfor each task, and maintaining a relationship between the parent taskand the child task for each occurrence in the pipeline.

Another object of the invention is to provide a hardware device forprocessing the tasks of a search algorithm in parallel wherein eachspecific task of the search is made by a dedicated processor.

The invention relates therefore to a hardware device for processing thetasks of an algorithm of the type comprising a number of processes theexecution of some of which depend on binary decisions, the devicecomprising a plurality of task units which are each associated with atask defined as being either one process or one decision or one processtogether with the following decision, and a task interconnection logicblock connected to each task unit for communicating actions from asource task unit to a destination task unit, each task unit including aprocessor for processing the steps of the associated task when thereceived action requests such a processing and a status manager forhandling the actions coming from other task units and building theactions to be sent to other task units

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the inventionwill be better understood by reading the following more particulardescription of the invention in conjunction with the accompanyingdrawings wherein:

FIG. 1 represents an exemplary algorithm composed of three processes andthree decisions.

FIG. 2 represents the algorithm illustrated in FIG. 1 which has beenstructured into several tasks to be executed by the hardware deviceaccording to the invention.

FIG. 3 is a block-diagram representing the hardware device according tothe invention.

FIG. 4 is a representation of the configuration register used to controleach task executed by the hardware device of FIG. 3.

FIGS. 5A and 5B are tables representing respectively the actions to beexecuted by each task of the algorithm illustrated in FIG. 1 in functionof the possible activation sources for an instance and the followinginstance.

FIG. 6 is a block-diagram representing the connection between the taskinterconnection logic block of the hardware device of FIG. 3 and thedifferent tasks of the algorithm.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary algorithm illustrated in FIG. 1 includes three processesP₁, P₂ and P₃ and two decisions D₁ and D₂. Depending on each decision,different functions corresponding to the different paths in thealgorithm may be run. The first function is represented by the algorithmflow when decision D₁ is “yes”, that is when processes P₁ and P₂ are tobe executed. The second function is represented by the algorithm flowwhen decision D₁ is “no” and decision D₂ is “yes”, that is whenprocesses P₁ and P₃ are to be executed. Finally, the third function isrepresented by the algorithm flow when decision D₁ is “no” and decisionD₂ is also “no”, that is when only process P₁ is to be executed. In thelatter case, the algorithm flow loops back to the entry point and thesame functions may be executed again. Thus, during the first algorithmflow, process P₁ is started while the execution of process P₁ is startedagain when decision D₂ is “no”. The second execution of P₁ starts onlyafter the first execution of P₁ has been completed and decision D₁ andD₂ have been completed. Therefore, there is no overlap possible in asimple step by step processing of the algorithm.

Though the algorithm represented in FIG. 1 is very simple, all thealgorithms are classically run in the same way. All the events(processes or decisions) of the algorithm flow have to be executed stepby step although they are run repetitively with new entry data. Theproposed invention allows the various processes and decisions to runseparately in order to speed up the processing of the algorithmespecially when there is no prior data required on some steps. The mainidea to achieve this is to have one processor assigned to a taskincluding a process, a decision or a combination of processes anddecisions which will run all the repetitive instances of this task andwill be linked to the execution result of the other task processorsusing a more detailed link information that the simple conventional linkenabling the downstream tasks to be activated.

Using the principles of the invention, the algorithm of FIG. 1 can bedivided into tasks as illustrated in FIG. 2. Four tasks are thusimplemented.

-   -   Task 1 (T₁) includes process P₂ (no decision)    -   Task 2 (T₂) includes process P₃ (no decision)    -   Task 3 (T₃) includes the sequential combination of process P₁        and decision D₁    -   Task 4 (T₄) includes only decision D₂ (no process)

According to the invention, each task is repetitively performed by oneprocessor allocated to this task. Therefore, four processors will berequired to run the example algorithm of FIG. 1 and FIG. 2.

The hardware device according to the invention illustrated in FIG. 3comprises as many task units 10, 12, 14 as the number of tasks includedin the algorithm (Task₁, Task₂ . . . Task_(n)). The interconnectionbetween the tasks is performed by the intermediary of a Taskinterconnection logic block 16 as explained hereafter.

Each task unit like task unit 10 includes a processor 18 in charge ofprocessing the sequential steps of the process, the decision or thecombination of the process and the decision generally incorporated inthe corresponding task. Actions received from other task units or sentto other task units by means of Task interconnection logic block 16 aremanaged by status manager 20 which is preferably a state machine. Statusmanager 20 is connected to processor 18 by two lines, an input line toprocessor 18 for starting (S) the task execution and the output linefrom the processor which is activated when the task is completed (C).

Status manager 20 has essentially two functions (input and output). Theinput function handles incoming commands from other tasks and the outputfunction builds commands to be sent to other tasks. To perform thesefunctions in conjunction with processor 18, several control/dataregisters 22, 24, 26 are used. Each control/data register corresponds,for this task, to an instance of the algorithm flow. The number ofinstances which can be run at the same time depends upon the pipelinecapability of processor 18. Generally, it is necessary to have threecontrol/data registers corresponding to instances m, m+1, m+2.

Each control/data register 22, 24 or 26 contains a control field and adata field. The control field is composed of three bits controlled byprocessor 18, a validation bit V, a completion bit C and a bit L/Rindicating whether the output is Left of Right when the task includes adecision.

The data field of a control/data register contains data which are loadedby status manager 20 after receiving an action to be performed fromanother task and before starting the task execution by sending the startcommand to task processor 18. These data may be used by processor 18.When the latter has completed the task execution, it may replace thedata contained in the control/data register by other data. This datawill then be sent to the destination task in the command word and usedas an input field by the destination task processor. However, it must benoted that, in case of independent tasks, the data are not modified inthe control/data register.

When the task execution has been completed by processor 18, this onesets to 1 the bit C of the control field of the control/data registerand a signal C may be sent to status manager 20. Therefore, eitherstatus manager is activated by the input signal C from task processor18, or there is a polling or an interrupt mechanism which enables thestatus manager to be informed of the setting of bit C to 1.

The commands which may be received from another task by status manager20 are START, KILL or VALID. As already mentioned, the START command isused to activate task processor 18. The KILL command means that a taskis no longer of interest since the taken decision is opposite to thistask. Thus, a task which is the left path of a decision may be killed ifthe decision is to take the right path. When it receives a KILL command,status manager 20 clears the control/data register corresponding to theinstance being considered as each command has as a parameter theinstance value called level. Conversely to the KILL command, the VALIDcommand confirms that the considered task corresponds to the takendecision. In such a case, the bit V of the corresponding control/dataregister is set to 1 by status manager 20.

The output function of status manager 20 is to build commands based onthe contents of two configuration registers, CONFIG.L 28 and CONFIG.R 30and also on the contents of the involved control/data register. Thecontents of CONFIG.L register which is selected when bit L/R set to 1are given in FIG. 4. Note that the CONFIG.R register which is selectedwhen bit L/R is set to 0 has exactly the same structure as CONFIG.Lregister. Note that the CONFIG.L and CONFIG.R registers are loaded atthe beginning of algorithm processing and remain unchanged insofar asthey contain data fields depending only on the algorithm structure.

As illustrated in FIG. 4, CONFIG.L register contains a first block Cselected when bit C is set to 1 and a second block V selected when bit Vis set to 1. Each block C or V is used for two actions. For each actionthe register contains the three following fields wherein X=C or V andn=1 or 2.

-   -   Task Xn indicates which task should be activated    -   Axn indicates which action is to be performed. For example        00=kill, 01=start, 10=valid and 11=valid+start.    -   Lxn indicates the level of task (the instance) corresponding to        Task Xn. For example, 00=current level−1, 01=current level,        10=current level+1, 11=current level+2.

The example of the algorithm illustrated in FIG. 2 will be consideredbelow. In FIG. 2 there are four tasks T₁, T₂, T₃ and T₄ which can beexecuted, but there are six activation sources since Task 3 and Task 4each have two outputs. Furthermore, a task acting as a source task canactivate a destination task in the same level or in the following level.FIG. 5A and FIG. 5B represent tables wherein the activation sources areassociated with the columns whereas the tasks to be activated areassociated with the rows. FIG. 5A corresponds to the activation of thetasks in a same level whereas FIG. 5B corresponds to the activation ofthe tasks in level m+1 by activation sources in level m. It should benoted that since only two levels are represented, this means that thereis no relationship between the processes of the algorithm on more thantwo consecutive levels.

In the tables illustrated in FIGS. 5A and 5B, only the casescorresponding to an action from an activation source to a task arefilled with a letter. Letter S means Start, V means Validate and K meansKill. It must be noted that it is possible that a same source has anaction on two tasks. Thus, T₃R kills Task 1, and starts and validatesTask T₄.

As already mentioned, status manager 20 (FIG. 2) uses the control bitswhich have been previously loaded in CONFIG.L and CONFIG.R registersassociated with the task. Thus, if we consider Task3 which generates twoactivation sources, the CONFIG.L and CONFIG.R registers have thefollowing contents:

CONFIG.L

-   1. Block C    -   Action 1 Task C₁=Task 3        -   AC₁=start        -   LC₁=current level+1    -   Action 2 none-   Block V    -   Action 1 Task V₁=Task 1        -   AV₁=valid        -   LV₁=current level    -   Action 2 none        CONFIG.R-   1. Block C    -   Action 1 Task C₁=Task 3        -   AC₁=start        -   LC₁=current level+1    -   Action 2 none-   2. Block V    -   Action 1 Task V₁=Task 1        -   AV₁=kill        -   LV₁=current level    -   Action 2 Task V₂=Task 4        -   AV₂=valid+start        -   LV₂=current level

The Task interconnection logic block 16 is represented in FIG. 6. Eachtask such as Task1, Task2, Task3, . . . Task n is an input to Taskinterconnection logic block 16 but is also an output to this block. Eachinput action or command could be of the same type as each one of theoutput actions such as KILL, START or VALID. Using the CONFIG.L andCONFIG.R registers where an action is represented by three controlfields Task Xn, Axn and Lxn, an action word may use this control fieldsin addition to the corresponding data (see FIG. 4) to transmit theaction to the destination task.

In the preferred embodiment illustrated in FIG. 6, the action wordcontaining the control bits of CONFIG.L or CONFIG.R registers and datais input to a three-state driver 40, 42, 44 or 46 where the Task Xnfield is decoded in order to select on which bus this action word shouldbe put. This word, or the remaining bits insofar as the Task Xn field isno longer used, are then decoded by the appropriate task to perform therequesting action.

As illustrated in FIG. 6, there are as many buses as the number oftasks. These buses are three-state so that all inactive inputs have noinfluence in the bus value. Only the valid one forced by thecorresponding driver takes the bus for its command. The width of the busdepends on the size of the action word. In the preferred embodiment thebus size is equal to word size. If there is a problem in the size of thebus, it is well known how to split the word into several blocks appendedwhen sent on a smaller bus. The only drawback of this split will be anincreased transmission latency as it will need several clock times totransmit a command or action from one output task to an input task. Atleast, the TaskXn should be available in the first block of the splitword to be decoded correctly.

Each task can then put all the actions on the various buses. As long asthere is no capability to have an action simultaneously put on the samebus by two tasks, there is no arbitration required. This is the case formost of the algorithms. Otherwise, an arbitration mechanism may be addedon the control of each three-state driver to identify two simultaneousrequests for the same destination. A very simple contention mechanismwill for example give the priority on the destination bus to the lowersource task.

1. The hardware device for concurrently processing a plurality of tasksassociated with an algorithm which includes a number of processes someof which are dependant on binary decisions, said device comprising: aplurality of task units for processing data, making decisions and/orprocessing data and making decisions; and a task interconnection logicmeans interconnecting the task units for communicating actions from asource task unit to a destination task unit; and each of said task unitsincluding a processor for executing the steps of the associated task inresponse to a received request action and a status manager for handlingactions from source task units and building actions to be sent todestination task units, wherein said actions communicated from a sourcetask unit to a destination task unit are START used to activate theprocessor of said destination task unit, KILL used to cancel the taskassociated with said destination task unit and VALID used to confirmthat task associated with said destination task unit corresponds to adecision included in said task, wherein said status manager activatessaid processor for processing the steps of the task associated with saiddestination task unit when the action received from a source task unitis START, and wherein each of said task units further comprises aplurality of control/data registers each corresponding, for the taskassociated with said task unit, to an instance of the algorithm flow,each one of said control/data registers comprising a control fieldcomposed of a completion bitset to 1 when the associated task iscompleted, a validation bit set to 1 when the associated task isvalidated and a L/R bit indicating that the output in the algorithm flowis left or right when said task includes a decision, and wherein each ofsaid control/data registers includes a data field which is loaded ifnecessary by said status manager activated by an action received from asource task unit, said processor using these data for executing the taskassociated with said task unit and replacing them if necessary.